I would vote for the closer position for the Q series and if you wanted to run a direct radiating speaker I would have said the farther position as there would be ample room for sound dispersion. I feel the farther away the Q's are from the listener you loose some impact from them due to their design, 3-4 ft is ideal for a QS and that 9' mark just might be too far, IMO.
Like the others have stated I would try to test it out at the various positions with a ladder and/or someone holding the speaker if necessary.
again, you bring up very valid points. i believe with proper calibration the QS in the back even at that distance will still make a good impact. yeah, i might have to raise the level of that channel a bit but the intent is to not necessarily have blairing sound firing out of the thing but to ensure that it's enough sound and it makes you get a true sense of depth in the surround field. yes i have no doubt that a direct radiating speaker would have done a great job. i do believe that what the QS offers is a much wider sound field overall.
i will try to do the test you mentioned and there is a way that i can temporarily hang the QS at the 4' mark to do the test. i promise to let you know which i like best and why.